Lightbulb



FIG. 1 is a front, right-side, and top isometric view of a lightbulb showing the new design.

FIG. 2 is a front elevation view of the lightbulb.

FIG. 3 is a left-side elevation view.

FIG. 4 is a right-side elevation view.

FIG. 5 is a back elevation view.

FIG. 6 is a top plan view; and,

FIG. 7 is a bottom plan view.

The broken lines near the top of the lightbulb represent structural elements that form no part of the claimed design. 

CLAIM The ornamental design for a lightbulb, as shown and described. 